The answer is a. Please explain how you approach this question and your answer

3. A company's ending inventory of finished goods has a total cost of $10,000 and consists of 500 units. If the overhead applied to these goods is $4,000, and the predetermined overhead rate is 80% of direct labor costs, how much direct materials cost was incurred in producing these 500 units? a. $10,000 b. $6,000 c. $4,000 d.$5,000 e. $1,000